Prior art seed blockage monitors indicate that a seed blockage has occurred in a seed flow path if signals produced by seeds flowing in the path are not generated within a given time period, if the seed flow rate falls below a predetermined rate, or if the seed flow rate decreases a certain amount in a given time period or during a given distance traveled by the air seeder. Examples of such prior art systems include U.S. Pat. No. 4,079,362 to Grimm, U.S. Pat. No. 5,177,470 to Repas and U.S. Pat. No. 4,491,241 to Knepler et al.